Somatosensory I Quiz

Somatosensory I

• Dr. Brian J. Piper, PhD MS
• Office hours: MW 2:15–3:15 & by appointment
• Location: 2018 MSB
• All course materials are copyright protected and restricted from further dissemination.

General Principles of Sensation

• Sensation is specialized for pain, touch, pressure and temperature.
• Intensity of stimulus relates to strength.
• Duration refers to the time of stimuli and adaptation.
• Location of the stimuli is key to identifying it.
• Sensation is not perception.
• Decussation is the crossing over of nerve fibers from one side of the brain or spinal cord to the other.

Thalamus

• Lateral Geniculate Nucleus: vision
• Medial Geniculate Nucleus: audition
• Ventral Posterolateral Nucleus: pain
• Anterior-Posterior: vestibular, taste, and various other functions

Co-Transmitters

• Amine/Amino Acid: dopamine, norepinephrine, epinephrine, serotonin, acetylcholine, GABA
• Neuropeptide: cholecystokinin (CCK), enkephalin, neurotensin, substance P, somatostatin, motilin

Substrates of Pain I

• Periacqueductal Gray (PAG)

  • Contains Substance P, which is an 11-amino acid neuropeptide that is co-released with other substances.
  • Contains enkephalins, which are opioid peptides.
  • Projects to the medulla (raphe magnus).

• Locus Coeruleus (Siegel: ceruleus)

  • Contains norepinephrine somas.
  • Projects to the dorsal horn of the spinal cord.

Substrates of Pain II

• Enkephalins bind to opiate receptors (metabotropic)
  • mu (μ): widely distributed in the brain (PAG, thalamus, striatum, locus coeruleus) and dorsal horn of the spinal cord. This is the main receptor.
  • Autoradiography is a histological technique to quantify receptor distribution.

Substrates of Pain III

• Enkephalins bind to opiate receptors (metabotropic)
  • delta (δ), kappa, and nociceptin opioid receptor (NOR-R) are more restricted in distribution than mu.
  • These receptors exhibit redundancy for mu.

Nociceptin

• Ligand: nociceptin (17 amino acids).
• PET (Positron Emission Tomography): highest in the caudate nucleus, lowest in the cerebellum.
• MRI: cortex and insula are found in areas of high nociceptin concentration.

Ascending Pathways

• Different red and blue pathways are used to illustrate the ascending pathways.

Somatosensory Homunculus

• A homunculus is a distorted representation of the human body, with the size of each part proportional to the amount of sensory cortex devoted to that part.

SI vs SII

• Primary Somatosensory Cortex (SI)
  • Function: pain representation (contralateral).
• Secondary Somatosensory Cortex (SII)
  • Location: dorsal surface of the lateral sulcus.
  • Function: pain recognition (bilateral).

Ascending Nociceptive Pathways

• Late Pain (C fibers)
  • 1: nociceptor to dorsal horn.
  • 2: cross over, ascend to thalamus (VPL).
  • 3: Anterior Cingulate Cortex (ACC) for the emotional component of pain.

Referred Pain

• Pain arising from the viscera is felt at the surface.
• The mechanism is unknown, but may involve the convergence of axons from internal organs and skin at the spinal cord.

Pain Syndromes

• Phantom Limb Pain: pain from a missing limb.
  • Treatment: mirror therapy.
• Opioid-induced hyperalgesia: increased pain sensitization among patients on chronic opioid therapy.
  • Mechanism is unknown.
  • Treatment: switch opioid or ketamine.
• Medication Overuse Headache: headache caused by overuse (>10 days/month) of various medications (triptans, caffeine, opioids).
  • Treatment: discontinue.

Acupuncture

• Study Design:

  • Chronic back pain patients (N = 638) completed a double-blind study with 6 licensed acupuncturists (4-19 years experience).
  • Study groups:
    • Individualized acupuncture
    • Standardized acupuncture
    • Sham acupuncture
    • Usual care
  • Impact Factor: IF = 16.5

Therapeutic Touch

• Why the study was done: To investigate whether therapeutic touch is an effective treatment option.
• What was done: A controlled study that compared therapeutic touch to a control group.
• What was found: Therapeutic touch did not produce any measurable effect.
• So?: Therapeutic touch is not a scientifically validated treatment method.
• Limitations: The study itself had limitations which need to be addressed in future research.
• Future directions: Further studies are needed to investigate the potential benefits of therapeutic touch.

Vancouver Referencing Style

• References are listed in numerical order.
• References appear in the same order that they are cited in the text.
• The reference list appears at the end of the paper.
• Abbreviate journals as they are listed in Pubmed.
  • Example: Journal of Neuroscience = J Neurosci
• Example: Piper BJ, DeKeuster RM, Beals ML, Cobb CM, Burchman CA, Perkinson L, et al.Substitution of medical cannabis for pharmaceutical agents for pain, anxiety, and sleep.J Psychopharmacolol. 2017; 31(5):569-75.

Selecting A Primary Research Article

• High Impact Factor (IF) Journal is preferred.
• Neuroscientific data with figures.
• Experimental design with a control group.
• Replication of previous findings is important.

Measuring Pain In Humans

• Key findings: Acupuncture was not found to be more effective than the control group in treating chronic back pain.
• Interpretation: Further research is needed to investigate the effectiveness of acupuncture as a pain management technique.